Never before has one tiny, lowly creature wreaked so much wrath on humankind. Blood sucking mosquitoes have cursed human populations the world over for centuries as carriers of disease, such as dengue fever, yellow fever, Rift Valley Fever, West Nile virus, Chikungunya virus, Japanese encephalitis, and most importantly, malaria. Approximately 250 million people around the world contract malaria annually, resulting in approximately one million human deaths every year. Man’s war with mosquitoes is relentless, yet these tiny pests continue to dominate, and so the fight against malaria continues.
An article published in Nature, ‘A World Without Mosquitoes‘, takes a very interesting look at the man versus mosquito debate. What makes even more interesting reading, however, are the comments that follow. This is a very controversial subject — on the one hand we are faced with an immense, and relentless, loss of human life every year, many of the victims being infants and children; on the other hand, the only truly effective methods used to control mosquitoes are extremely damaging to the environment. This proves to be quite a moral dilemma – do we save people at the expense of the environment, or do we protect the environment at the expense of human lives?
Malaria is a disease that is caused by the Plasmodium parasite, which is transmitted to a host by mosquitoes of the Anopheles genus, who act as a vector of the disease without becoming infected themselves. Malaria is rife in the tropics and sub-tropics, particularly in Sub-Saharan Africa, Asia, and South America. According to the Centers for Disease Control and Prevention, half the world’s human population live in areas where malaria infection poses a risk to their health. People living in Sub-Saharan African countries are most at risk, with nearly 90% of malaria deaths occurring in this region, where it is the second highest cause of death, following HIV/AIDS.
Effective methods used for the control of malaria carrying mosquitoes include spraying with insecticides, and draining wetlands that contain stagnant pools or ponds of water – neither of which are environmentally sound practices. Use of insecticide impregnated mosquito nets help to keep mosquitos at bay, and when available, drastically reduces risk of infection. The notorious insecticide, DDT (Dichloro-diphenyl-trichloroethane) – which won its inventor, Dr Paul Muller, a Nobel Peace prize in 1948 – was used extensively to rid the United States of malaria. But the use of this chemical insecticide comes with a hefty price to the environment, as attested to in the classic book ‘Silent Spring‘, written by biologist, Rachel Carson, first published in 1962.
DDT accumulates in the fatty tissues of living organisms, and becomes more concentrated up the food chain. Consequently, animals further up the food chain are also affected by the toxins. While these may not kill higher organisms outright, the damage is subtle, but far more sinister in the long term. DDT is known to reduce fertility, feminize male organisms, cause birth defects, and reduce breeding success. As DDT largely affects sex hormones and reproductive organs, it can negatively affect fertility, reproduction, and ultimately species survival.
One also needs to consider the ecological role of mosquitoes – if they were totally eradicated, how would this impact food web dynamics and ecosystem functioning? Would it have other ramifications? While some may argue that human life should be considered far more valuable than that of other animals, others may disagree. Furthermore, many of these human populations also depend on this wildlife as a source of food, including fish, water fowl and mammals that are supported by the mosquito and its larvae at the base of the food chain. More importantly, though, mosquitoes are able to build up resistance to DDT, which effectively gives rise to a generation of ‘super’ mosquitoes that cannot be killed with this most potent of toxins. While research has shown that DDT is effective at repelling resistant mosquitoes, it doesn’t actually eradicate them, they just avoid huts sprayed with DDT, and move on to find a victim at the hut next door.
While DDT is now largely banned in most parts of the world, it is still used to combat malaria in some African countries, and despite its drawbacks, it has many supporters who advocate its use in the fight against malaria.
The World Health Organization (WHO) issued a statement in 2006 that supported the controlled use of DDT to combat malaria. However, after conducting research to assess the health risks associated with use of DDT inside homes, they have since changed their tune. In 2011 WHO published a report on their findings regarding the health risks of DDT. According to their report, young women of child bearing age are most at risk, and can pass DDT on to their unborn child in the womb, or while breastfeeding their babies. Exposure to DDT can cause a number of negative health effects in humans – it can cause hormonal imbalances, infertility, birth defects and genital deformities, breast cancer, brain damage in the developmental stages, and diabetes. Children exposed to high levels of DDT can suffer convulsions and even death. These findings pretty much echo the known effects of DDT on wildlife.
Using DDT in the fight against malaria is truly a case of ‘you’re damned if you do, and you’re damned if you don’t’. But all said and done, is it not better to research new innovative measures to combat something that we fully understand, rather than take the easy option in the short term, without fully comprehending the long-term effects on both the environment, and the human populations that we are trying to protect? Especially considering that the long-term effects are largely unknown, and may be even more devastating than malaria itself.